Such extending systems are used for example for covering guideways of a machine tool in order to protect them against contamination during operation of the machine tool. An example of known extending systems of the type described in the introduction is shown schematically in FIG. 6 in the form of a telescopic steel cover for a guideway of a machine tool. This system has four extending elements 110, 120, 130 and 140 in the form of cover elements designed to cover a guideway 160 of a machine tool as well as a scissor-like coupling arrangement 150. The cover element 110 is fixed on a frame 105 of the machine tool, whilst the cover element 140 is coupled to a processing tool (not shown) of the machine tool, the said processing tool being capable of travelling along the guideway 160. The coupling arrangement 150 has two coupling rods 152, 152a respectively which are met rotatably on a link pin 112 fixed on the front end of the cover element 110, the said coupling rods being articulated at their ends remote from the link pin 112 by way of hinge joints 153, 153a respectively on coupling rods 154, 154a respectively which are set rotatably on a link pin 122 fixed on the front end of the cover element 120. The coupling rods 154, 154a respectively are articulated at their ends opposite the hinge joints 153, 153a respectively by way of hinge joints 155, 155a on coupling rods 156, 156a respectively which are set rotatably on a link pin 132 fixed on the front end of the cover element 130. Finally, these coupling rods 156, 156a respectively are articulated by way of hinge joints 157, 157a disposed at the ends of the said coupling rods opposite the hinge joints 155, 155a respectively on coupling rods 158, 158a respectively which are set rotatably on a link pin 142 fixed on the front end of the cover element 140.
When the processing tool coupled to the cover element 140 is moved in the direction denoted by the arrow 170 along the runway 160 in order to carry out required processing, the cover element 140 is entrained. As a result the cover is drawn apart out of the inserted position shown in FIG. 6 in which the cover elements 110, 140 respectively are inserted telescopically into one another. In this case the coupling arrangement 150 provides that the extending movement triggered by the movement of the processing tool is uniformly distributed over the extending elements 120, 130 and 140, so that the extension distance of the cover element 140 relative to the cover element 130 in each phase of the extending movement corresponds to that of the cover element 130 relative to the cover element 120 and to that of the cover element 120 relative to the cover element 110. Such a coupling ensures a disruption-free extending movement over all of the available extension length.
Depending upon the dimensions of the cover elements, however, it may be necessary for this purpose to use scissor-like coupling elements of the type shown in FIG. 6, the dimensions of which in a direction extending perpendicular to the direction of extension 170 exceed the dimensions of the cover elements in this direction. Therefore extending systems of the type shown in FIG. 6 cannot be used in confined installation conditions. Furthermore, in the case of an insertion movement out of the extended position reached due to the extending movement in the direction denoted by the arrow 170, considerable forces are exerted on the link pins fixed on the cover elements as well as the link rods and hinge joints of the coupling arrangement 150, which results in severe wear of extending systems of the type shown in FIG. 6.
In view of this problem a telescopic cover of the type shown schematically in FIG. 7 was developed. This telescopic cover has three cover elements 210, 220 and 230 and a coupling arrangement 250. The cover element 210 is fixed on a frame 205 of the machine tool, whilst the cover element 230 can be coupled to a processing tool (not shown) of the machine tool. The coupling arrangement 250 of the arrangement shown in FIG. 7 has a chain 256, which runs round two return spindles 252 and 254 which are fixed relative to the cover element 220 and extend perpendicular to the direction of extension denoted by the arrow 270, as well as two two entraining elements 212 and 232 which are coupled to coupling regions of the chain 256 which are opposite one another. The entraining element 212 is fixed on the cover element 210, whilst the entraining element 232 is fixed on the cover element 230.
In the case of an extending movement of the cover element 230 in the direction denoted by the arrow 270 the entraining element 232 is moved relative to the cover element 220 in the direction denoted by the arrow 257, whilst the entraining element 212 is moved relative to the cover element 220 in the direction denoted by the arrow 258. Because of the fixing of the entraining element 212 on the cover element 210, which for its part is fixed on the machine frame 205, at any time in the extending movement the extension distance of the cover element 230 relative to the cover element 220 corresponds to that of the cover element 220 relative to the cover element 210. In this way it is also possible using the coupling arrangement 250 to ensure a disruption-free extending movement over all of the available extension length. Furthermore, the coupling arrangement 250 hardly takes up any space. Finally, the turning movement of the chain 256 which is required in order to couple the extending elements 210 to 230 can be effected both in the direction of extension denoted by the arrow 270 and in the direction of insertion which is opposed thereto, without significant exertion of force, so that the coupling arrangement 250 is not subject to any significant wear.
However, the coupling arrangement 250 shown in FIG. 7 can only be used For coupling in all of three extending elements. Therefore in the inserted position the length of an extending system provided with such a coupling arrangement amounts to at least a third of the maximum extension length which can be achieved in the extended position. Therefore the extending system shown in FIG. 7 cannot be used when a great extension length and the smallest possible dimensions in the inserted position are required simultaneously. However, even if the dimensions in the inserted position are not subject to any particular restrictions the extending system shown in FIG. 7 can lead to problems in manipulation if a great extension length is required, because then very large extending elements which are difficult to manipulate are required.
In view of the problems just described, extending systems of the type shown schematically in FIG. 8 are used nowadays if great extension lengths and the smallest possible dimensions in the inserted position are required simultaneously. The extending system shown in FIG. 8 in the form of telescopic cover for a guideway 360 of a machine tool comprises four cover elements 310, 320, 330 and 340 which are pushed telescopically into one another in the inserted position shown in FIG. 8. The cover element 310 is fixed on a machine frame 305, whilst the cover element 340 can be coupled to a processing tool or the machine tool and when the latter moves along the guideway 360 the cover element 340 can be entrained thereby. At the rear ends of the cover elements 320, 330 and 340 are disposed entraining elements 322, 332, 342 which cooperate with stop elements 314, 324 and 334 disposed on the front ends of the extending elements 310, 320 and 330.
When the processing tool (not shown) of the machine tool moves in the direction denoted by the arrow 370 the cover element 340 is first of all entrained independently of the cover elements 310, 320 and 330, until the entraining element 342 disposed on the rear end of the cover element 340 strikes the stop element 334 disposed on the front end of the cover element 330 and thus entrains the cover element 330. As the extending movement progresses the entraining element 332 disposed on the rear end of the cover element 330 strikes the stop element 324 disposed on the front end of the cover element 320 and thus entrains the cover element 320. Finally the extending movement is stopped when the entraining element 332 disposed on the rear end of the cover element 320 strikes the stop 314 disposed on the front end of the cover element 310.
With an extending system of the type shown in FIG. 8, even with very great maximum extension lengths, almost any small dimensions can be achieved in the inserted position. However, due to the impacts of the entraining elements 342 and 332 on the stop elements 334 and 324 respectively, such strong vibrations are generally exerted on the processing tool coupled to the cover element 340 that marked impairments of the processing quality can occur at the corresponding locations of the workpiece processed with the processing tool. In order to eliminate these shortcomings it has already been proposed that the entraining elements or stop elements of extending systems of the type shown in FIG. 8 be provided with damping elements. With these damping elements the vibrations triggered by the impacts can still be adequately damped at rates of extension of up to 40 m per minute. However, with modern machine tools travelling speeds of the processing tool during processing of 100 m per minute or more can be reached. Therefore the maximum processing speed which can be achieved without impairing the processing quality is limited by the maximum rate of extension of the extending systems required to cover the guideway of the machine whilst ensuring sufficient vibration damping.